A plug-in hybrid electric vehicle (PHEV) has more than one source of power. An electric machine may be configured to propel the vehicle and uses a battery as a source of energy. The battery may be recharged using an external power source, such as a charging station. An engine may also be configured to propel the vehicle and use fuel as a source of energy.
The PHEV may operate for long periods of time using only battery power, for example, when the PHEV is used for shorter commutes, trips, and the like. The battery is recharged between these trips using a charging station and does not reach a state of charge where engine power is required to propel the vehicle. Fuel in the fuel tank may degrade or become stale during these periods of time of the vehicle operating using primarily battery power. In some instances, this may lead to fuel degradation such as acid formation in the fuel, waxing with olefin formation, and the like.